1. Field of the Invention
This invention generally relates to thermoplastic processing and, more particularly, to a process for producing a polymer coating on fabric materials and other porous substrates.
2. Description of the Related Art
Thermoplastic coatings have long been applied to fabrics. These thermoplastic coatings are often used to produce waterproof, but breathable, fabrics. Waterproof/breathable fabrics are then used in the design and manufacture of waterproof rain gear and other waterproof outerwear.
One method of producing thermoplastic coatings on fabrics is called film or sheet-lamination. This method bonds a thin film or sheet of thermoplastic material to a fabric. The sheet-extrusion process uses a conventional extruder to produce the hot thin sheet of thermoplastic material. The fabric material is then overlaid onto the hot thin sheet of thermoplastic material. Because the thin sheet of thermoplastic material is still hot from the extruder, the thin sheet of thermoplastic material should ideally bond and stick to the fabric material. This process does not provide the best adhesion between the two layers, and only gives surface tac-weld. Thus, it can be delaminated with little effort.
Another commonly-used method to produce thermoplastic coatings on fabrics is called xe2x80x9cknife-over-roll.xe2x80x9d This method is also used to apply a thin sheet of elastomeric polymer onto a fabric. The knife-over-roll method melts the elastomeric polymer material. A special tool, or xe2x80x9cknife,xe2x80x9d applies a thin layer of the melted elastomeric polymer material onto the roll and is then transferred onto the fabric. The elastomeric polymer material cools and produces a thin sheet of polymer on the fabric material.
A third commonly-used method is a xe2x80x9cdropxe2x80x9d method. The elastomeric polymer material is melted and then simply xe2x80x9cdroppedxe2x80x9d onto the fabric material. A roller or scraper tool is then used to smooth the melted elastomeric polymer material into a thin sheet.
A fourth method applies solvent based adhesive on the fabric. A layer of film is then laminated on it through the application of heat and pressure. The adhesive serves to increase bonding and peel strength between fabric and film.
U.S. Pat. No. 4,496,508 to Hartmann et al. is an example of fabrics with bonded polymer coatings. Hartmann et al. describes extruded polypropylene filaments that are bonded to a porous fabric. The bonded polypropylene filaments thus provide a spun-bonded fabric. Again, however, the polypropylene filaments are bonded and, thus, easily peeled away from the underlying porous fabric. Hartmann et al. also utilizes polymer filaments, and these filaments are costly to place and to bond to the porous fabric.
There is, accordingly, a need in the art for a process which does not require an adhesive layer between fabric and polymeric film, a process which can utilize a variety of thermoplastic/polymer materials, and a process which is always cost effective to implement.
The aforementioned problems are resolved by a process for producing a polymer coating penetrating a porous substrate. The process of the present invention allows the polymer coating to penetrate the porous substrate and produce a composite polymer-penetrated porous substrate. The process includes the steps of continually extruding material onto a roll of two to three roll stack, and on that film, overlaying fabric or porous substrate. As the film is tac-welded to the porous substrate, enough heat is maintained and vacuum is applied to draw the heated film of polymer material onto the porous substrate. The process produces a polymer coating that penetrates and adheres to the porous substrate.
The process of the present invention is applicable to all porous substrates. The porous substrate, for example, may utilize cotton fabrics, silks, wools, and even polymer blends such as polyesters, rayons, etc. The process of the present invention may utilize other porous substrates, such as metal wire materials, carbon filament materials, and glass filament materials. The process is also applicable to perforated substrates, such as perforated vinyl, perforated leather, and perforated suede. The present invention is applicable to clothing fabrics, carpets, rugs, outdoor floor coverings and awnings, and other fabric products where waterproofing is desirable.
An alternative process for producing a polymer coating on a porous substrates is also disclosed. The process includes the steps of interposing a film of polymer material between a first porous substrate and a second porous substrate. The film of polymer material is heated and vacuum drawn into the first porous substrate and into the second porous substrate.
A product made according to a process is also disclosed. The product includes a porous substrate and a polymer coating penetrating and adhering to the porous substrate. The polymer coating is formed by continually extruding a film of polymer material onto the porous substrate. The film of polymer material is heated and vacuum drawn into the porous substrate.
A product is also disclosed. The product includes a first porous substrate and a polymer coating penetrating and adhering to the first porous substrate. The product may also include a second porous substrate, and the polymer coating penetrates and adheres to both the first porous substrate and the second porous substrate.
An apparatus for producing polymer coatings on a porous substrate is disclosed. The apparatus includes an extruder, die, means for overlaying film on top or bottom of the porous substrate, means for heating a film of polymer material and at least one vacuum unit. The one vacuum unit draws the heated film of polymer material into the porous substrate. The apparatus may further include means for overlaying the porous substrate and the film of polymer material.